Cough is a most common chief complaint which troubles outpatients of the respiratory department. Cough is a defensive reflex activity, and physiological cough is a beneficial action. However, long-time frequent or too drastic cough is a pathological reaction, which not only increases the pain of patients, affects rest and sleep and increases physical power consumption, but also promotes the development of diseases and generates other complications when the cough is serious.
Asarum, which is a traditional Chinese medicine, has over thousands of years of use history. Asarum was initially recorded in Shennong's Herbal and was listed in a top grade. Chinese Pharmacopoeia (2010) stipulates that asarum is derived from dried roots and rootstocks of Aristolochiaceae plant-Asarum Heterotropoides Fr. Schmidt var. mandshuricum (Maxim.) Kitag., asarum sieboldii Miq. var. seoulense Nakai or Asarum sieboldii Miq, asarum is warm in nature, acrid in taste and good for heart, lung and kidney meridians. Asarum has effects of relieving exterior syndrome and dispelling cold, dispelling wind and relieving pain, orifice freeing, and warming the lung and dissipating excessive fluid and is used for treating cough and asthma due to phlegm and retained fluid, common cold due to wind-cold, headache, toothache, nasal obstruction and running nose, allergic rhinitis, nasosinusitis and rheumatic arthralgia. A literature has reported that asarum volatile oil has an antitussive activity and the main effective component is considered as methyleugenol in the volatile oil (Zhou Huiqiu, Research on Pharmacological Action of Methyleugenol, Journal of Chinese Medicine and Pharmacology, 2000, (2):79-80). asarinin is known as a high-content non-volatile constituent in asarum (Han Junyan, Research Progress of Traditional Chinese Medicine asarum, Chinese Agricultural Science Bulletin, 2011, 27(9):46-50), is mainly contained in Aristolochiaceae plant-Asarum Heterotropoides Fr. Schmidt var. mandshuricum (Maxim.) Kitag., Asarum sieboldii Miq. var. seoulense Nakai and Asarum sieboldii Miq., and is the quality control component of asarum recorded in Chinese Pharmacopoeia (2010). The existing literatures report that asarinin is obtained by an extraction method in Manual of Extraction and Separation of Chemical Components of Traditional Chinese Medicine edited by Yang Yun in 1998. The method comprises: ethanol-thermal extraction, steam distillation, extraction with diethyl ether, recrystallization with ethanol and the like. Therefore, the process is complex. Meanwhile, heating treatment is needed in the extraction process, which easily causes unstable components of traditional Chinese medicine. Toxic organic reagents, such as Pb(OAC)2, H2S, ET2O and the like, need to be added in the process, thereby causing the problem of residue of the organic reagents. Therefore, asarinin is not suitable for industrial mass production.
Asarinin is a lignans compound, research reports on asarinin are fewer, and a research has indicated that asarinin has immunosuppressive effect and can be used for anti-transplant rejection (Zhang Lili, Function of Acute Rejection of Heart Transplantation and Influence on Expression of Adhesion Molecules of Asarinin, China Journal of Chinese Materia Medica, 2006, 31(06):494-497.). The research finds that asarinin has a better antitussive function for a citric acid induced guinea pig cough model; and a research report on an antitussive activity of asarinin has not been seen so far, and a report on a method for preparing asarinin directly from the asarum volatile oil by an SFE-CO2 method has also not been seen.